为什么这个程序生成的全是除法

Question

#include
#include
main()
{
int a, b, c,e,i = 1, k = 0, j = 0, n,s;
char d;
printf("请输入要做的题目数目：");
scanf("%d", &n);
while (i <= n)
{
srand(time(NULL));
a = rand() % 100 + 1;
b = rand() % 100 + 1;
c = rand() % 4 + 1;
{
if (c = 1)
d = '+';
if (c = 2)
d = '-';
if (c = 3)
d = '*';
if (c = 4)
d = '/';
}
switch (d)
{
case '+':e=a + b; break;
case '-':e=a - b; break;
case '*':e=a * b; break;
case '/':e=a / b; break;
}
printf("%d%c%d=", a, d, b);
scanf("%d", &s);
if (e==s)
{
printf("答案正确！\n");
j++;
}
else
{
printf("答案错误！\n");
k++;
}
i++;
}
printf("正确：%d个,错误：%d个", j, k);
switch (j)
{
case 0:
case 1:
case 2:
case 3:
case 4:
case 5:printf("不及格，还需继续努力！\n"); break;
case 6:
case 7:printf("及格，还不错！\n"); break;
case 8:
case 9:printf("良好！\n"); break;
case 10:printf("优秀，你真棒！\n"); break;
}
}

Answer 1

兄弟，你的c=1以及后面的应该是c==1吧，你写成赋值语句了